Aluminum and magnesium are common structural metal with high commercial interest.
Pure aluminum (Al) is a silver-white, malleable, ductile metal with one-third the density of steel. It is the most abundant metal in the earth's crust. Aluminum is an excellent conductor of electricity and has twice the electrical conductance of copper. It is also an efficient conductor of heat and a good reflector of light and radiant heat.
Unlike most of the other major metals, aluminum does not occur in its native state, but occurs ubiquitously in the environment as silicates, oxides and hydroxides, in combination with other elements such as sodium and fluoride, and as complexes with organic matter. When combined with water and other trace elements, it produces the main ore of aluminum known as bauxite.
Magnesium compounds, primarily magnesium oxide (MgO), are used as a refractory material in furnace linings for producing iron, steel, nonferrous metals, glass and cement. Magnesium oxide and other magnesium compounds are also used in the agricultural, chemical, automobile, aerospace and construction industries.
Presently, aluminum is produced by separating pure alumina from bauxite in a refinery, then treating the alumina by electrolysis using the Hall-Heroult and Bayer processes. An electric current flowing through a molten electrolyte, in which alumina has been dissolved, separates the aluminum oxide into oxygen, which collects on carbon anodes immersed in the electrolyte, and aluminum metal, which collects on the bottom of the carbon-lined cell (cathode). On average, it takes about 4 t of bauxite to obtain 2 t of aluminum oxide, which in turn yields 1 t of metal. For over 120 years, the Bayer process and the Hall-Heroult process together have been the standard commercial method of the production of aluminum metal. These processes require large amounts of electricity and generate undesired by products, such as fluorides in the case of the Hall-Heroult process and red mud in the case of the Bayer process.
The production of aluminum by electrolysis of aluminum chloride has been a long-desired and theoretically feasible objective; the economic attainment thereof has never become an economic reality. Among the many reasons therefor are numerous unsolved problems occasioned, for example, the highly corrosive chlorine vapors or gases emanating from the electrolysis, as well as the complex salts or eutectics of the bath components and the products of electrolysis, all of which will be herein broadly encompassed by the term electrolyte, are of corrosive character and apparently compound the problem. Among such problems are the short life of cell components and the detrimental contamination of the bath through reaction thereof with the confining environmental elements in the electrolytic cells.
Taking out the magnesium metal from unrefined materials is a force exhaustive procedure requiring nicely tuned technologies. Presently, to extract magnesium, an electrolysis process is generally used. The tailings are leached in hydrochloric acid, creating a brine from which the magnesium is extracted using electrolysis. Thermal lessening of magnesium oxide is also used for extracting magnesium from ores.
Conventionally, during the course of electrolytic production of magnesium, chlorine gas is formed at the anode (metallic magnesium being formed at the cathode). Conventional anodes used in such process are made of graphite. At the high temperatures involved, the chlorine gas tends to attack the graphite anode and various chlorinated carbon compounds may be formed. The chlorine gas itself and the chlorinated carbon compounds are environmentally hazardous and are difficult to remove and are expensive to deal with. In addition, because the graphite anode is slowly consumed by this reaction, the anode itself must be periodically replaced, at not an insignificant expense.
There is thus still a need to be provided with improved processes for extracting metals such as aluminum and magnesium.